This invention relates to musical instruments and, more particularly, to a musical keyboard instrument having an automatic playing capability.
For many years the player piano has been a well known musical instrument having an automatic playing capability. Player pianos traditionally utilize paper rolls having punched hole information therein, the punched hole information being read by a device in the player piano which, in turn, activates appropriate keys thereof. Typically, the positions of each row of holes in the paper correspond to keys to be activated at a given instant. In most respects, the paper roll technique has become obsolete, the paper rolls being cumbersome and fragile, and generally not having the information carrying capability to effect quality reproductions of a sophisticated musical performance. Also, it has not been possible for the user of the player piano (or other keyboard instrument) to record his or her own musical performance for later playback.
There have recently been developed a number of systems which are capable of recording, typically on magnetic tape, and key actuations of a musical performance on a keyboard instrument, generally an electronic musical instrument such as an electronic organ. With these systems it is possible for the user to record his or her musical performance on magnetic tape for subsequent playback. Playbacks is in the manner of a player piano and allows musical reproduction by the instrument which is of much greater quality than if the audio had itself been recorded on magnetic tape in conventional analog fashion. In addition to entertainment advantages, these systems are useful as teaching aids or selling tools, and conventional audio can be provided, for various purposes, on a separate track of the magnetic tape. Systems of the described type are disclosed, for example, in U.S. Pat. Nos. 3,604,299, 3,610,799, 3,683,096, 3,829,597, and 3,905,267.
The most prevalent scheme used for recording the instrument key actuations is to provide a basic "cycle" or "frame" rate of, say, 100 cycles per second. During each cycle, each key of the keyboard (as well as other information such as the positions of "stops" and the instrument loudness or "expression") is interrogated, and a special signal is generated for each key that is determined to be active during the cycle. For example, in a "time division multiplexing" scheme disclosed in some of the above-referenced patents, the keys are sampled in a specified sequence with each key having its own "time slot" during the cycle. Thus, for example, if there are 100 keys (including the keys themselves plus stop, switches, etc.), there would be 100 time slots, with a relative position of each time slot in the sequence uniquely representing the activation (or non-activation) of a key. Using this example, if there are 100 cycles (or frames) per second, and 100 time slots per cycle, then a bit frequency of 10 KHz would be necessary to represent and record, in digital form a musical performance. Actually, a somewhat higher bit frequency would be necessary since a portion of the frame may be needed for recording synchronizing information (e.g., to separate cycles or frames from one another).
The described systems, and other prior art techniques, are believed to provide less than optimum performance for various reasons. First, for the number of keys being encoded, the basic frequency requirements are believed to be unnecessarily high. Since the signal is typically to be recorded on limited quality magnetic tape equipment (e.g., a standard tape cassette system), it is desirable to keep the bit frequency requirements as low as possible so as to minimize the problems associated with storing digital information on tape and faithfully recovering the information. The basic frequency of operation could, of course, be lowered by lowering the cycle (or frame) rate; i.e., the rate at which the keys are interrogated. However, it must be insured that this does not result in the user being able to "outplay" (i.e., play faster than) the equipment, a factor which depends upon the playing efficiency of the user. Summarizing considerations of bit frequency: for a given number of keys and a given level of user proficiency, it is desirable to employ a coding rationale which utilizes a bit frequency that is as low as possible.
Once an encoding rationale has been devised, it is necessary to put the information in a form that is suitable for recording on the recording medium, typically magnetic tape. The information should be recordable and recoverable in a manner which is efficient and also not susceptible to errors caused by the recording or recovery processes. Also, in the event an error occurs, it is desirable that the system handle errors in a way which is least disturbing during playback.
It is among the objects of the present invention to provide solution to the types of problems set forth and to generally provide an improved musical keyboard instrument having an automatic playing capability.